Update permanently redirected feeds to their new location

Clients with link editing capabilities ought to automaticallyre-link references to the effective request URI to one or more of the newreferences returned by the server, where possible.

This means, that when a feed address returns a permanent redirect, Newsblur should update the feed subscription address and don’t repeat the request to the redirected address. This will help prevent loss of feeds when sites move domains and redirecting cross domains or change publishing systems. After some time, old redirects and addresses eventually become unmaintaned. Newsblur should update addresses as informed by server. Plus, this should speed up feed retrieval somewhat as all the meaningless redirects that probably many feeds go through today will be cut out of the picture. Will also help canonical feed addresses and subscription counts for publishers.

This does not apply to 302 and 307 temporary redirects.

PS: It can be prudent — but not required by any RFC — to confirm that the redirect is still in place like a week or month after automatically re-linking. Servers and sysadmins can make honest redirect mistakes.